However, Biden's position alone does not end the deal. The transaction is currently being reviewed by the Committee on Foreign Investment in the US, and the White House has not yet indicated that Biden will directly intervene in this ongoing review process.

The main obstacle to the transaction is the opposition of the United Steelworkers union to the sale. Their members, particularly in key Midwestern swing states such as Pennsylvania and Wisconsin, have considerable influence and can influence the outcome of the upcoming November presidential and Senate elections.

Nippon Steel entered into an agreement to acquire US Steel for US$14.9 billion last December. The acquisition would create the world's second-largest steel company, and as part of its offer, Nippon Steel also committed to invest US$1.4 billion to upgrade U.S. Steel's aging mills.

Founded in 1901 by industrial magnates Andrew Carnegie and JP Morgan, US Steel was one of the world's largest companies at its height, thriving on American expansion and industrial progress. As in the wider US steel industry, however, its leadership has gradually waned over the years due to increasing competition from more affordable foreign sources. It currently employs more than 22,000 people worldwide, including more than 14,000 in the United States.